Cemented metallic bodies (“CMBs”) are structurally strong and have good wear resistance under extreme environment, such as shear, abrasion, friction, and heat. Due to these advantages, CMBs are utilized for high-speed cutting or drilling tools, for molding dies, and for wear resistance components. A particularly important application is a CMB's use in the manufacture of ultra-hard compacts, such as polycrystalline diamond composites (“PDCs”) and polycrystalline cubic boron nitride (“PcBN”).
A particularly important CMB is the metallic-tungsten carbide (“m-WC”) material used as the substrate of PDCs. PDCs are generally used as drilling tools that are expected to be put under extreme shear, high friction, severe abrasion, and internal forces. PDCs are generally a construction of two components: a diamond plate and its attached substrate. Such an ultra-hard compact is generally prepared in two steps. First, the m-WC substrate is normally prepared by hot isostatic pressing (“HIP”), sintering around a 6-20 weight percent loading of tungsten carbide (“WC”) powder into metallic catalyst matrix—such as cobalt—under isostatic gas pressure. In HIP, the temperature of m-WB mixture is increased to the melting point of the metallic catalyst matrix component, and the metal matrix melts. Yet tungsten carbide grains, due to a relatively higher melting point, remain in the solid phase. As a result of this process the matrix embeds and cements the carbide grains thereby creating a hard material with distinct material properties. As a second step, diamond powder is placed in a PDC press mold and sintered while the m-WC substrate is placed on top of the powder in the PDC mold, sintering takes place under a high-pressure, high temperature process (“HPHT”) by a PDC press mold in a sintering device. When the substrate metallic catalyst matrix melts in the HPHT sintering operation, it partially sweeps (i.e., penetrates interstitial spaces) from the substrate into the plate, creating a two-layer composite with a single matrix combining the two components: the plate having diamond grains wet by metallic catalyst matrix and the substrate being substantially only m-WC, with a lower concentration of matrix due to some portion of it sweeping into the plate. The metallic catalyst promotes a carbon-carbon reaction between diamond grains that result in sp3 hybridized carbon bonds between adjacent diamond grains, thereby creating an ultra-hard diamond skeleton in the plate.
A conventional end product is shown in FIGS. 1 and 2. PDC 100 comprises a diamond plate 110 and a substrate 120. The diamond plate has a rake 114—that is not responsible for cutting but instead helps remove cut material—and flank 112, which performs abrasion. The diamond plate 110 and the substrate have an interface 130.
The construction is composed of two layers, the top layer is a PDC layer (i.e., the plate), which has been sintered to a substrate, thereby sharing a matrix phase. The plate is utilized for cutting or drilling operations, and the substrate is used as a shock absorber and an interface between the plate and the rest of a tool. In the case of a braze joint, the interface is stronger between two metallic components, and therefore the nature of the substrate becomes critical when attaching it to other components.
One significant problem with conventional PDCs is that as the temperature and pressure of the process is reduced back to atmospheric conditions at the end of the manufacturing operation the PDC cools but the cobalt matrix and diamond grains have different coefficients of thermal expansion (“CTE”), which results in different amounts of volume change in between the diamond grains and the interstitial spaces. The net result of this effect is internal stress being built up within the PDC itself. Like all such processes, a dynamic energy minimum is achieved. While the diamond-particle-to-diamond-particle bonds are strong, significant stress exists within the plate and extreme stress generally exists at the interface between the plate and the substrate. When in use PDCs are exposed to abuse, such as abrasion, shear, and friction- and environment-induced high temperatures, such as 700° C. or even higher, which exacerbates an already significant amount of residual stress. Therefore during use when the PDC has higher energy to break bonds, these internal stresses, shear, and abrasion synergize in an unfavorable manner that can cause micro-cracks, which over time degrade the product, potentially causing fracture or total failure. Of all the synergizing effects, it is believed that temperature has the largest influence over the product's failure. In order to overcome this deficiency, fabrication of a thermally stable polycrystalline compact (“TSP”) is desirable.
One conventional method to fabricate it TSP is using a catalyst that has a similar CTE as diamond. Silicon is the most common catalytic matrix. Silicon reacts with the diamond during the high temperature and high pressure step of compact sintering to form silicon carbide links between diamond particles. Both silicon and silicon carbide exhibit a CTE relatively similar to diamond. Therefore, the resultant compact is considered thermally stable because it can withstand temperatures as high as 1100° C. without significant deterioration of abrasion or shear resistance. (See U.S. Pat. No. 8,020,644, which is incorporated herein by reference.) However, PCD made utilizing silicon as a binder does not have similar properties to PCD made utilizing catalytic cobalt. Instead of forming diamond-to-diamond sp3 bonds between adjacent diamond grains (through bridges based on carbon-carbon bonds), the large majority of diamond grains are attached to each other through silicon bridges based off of silicon-carbon bonds. While carbon atoms at the surface of adjacent diamond grains may still form carbon-carbon bonds due to limited graphitization, silicon acts as the major bridge linking the diamond grains together. Silicon-carbon bonds have significantly less strength than the carbon-carbon sp3 bonds. Hence despite the fact that heating has a lower relative effect on the performance of the compact and a TSP is indeed fabricated because the PDC is thermally stable, because the carbon skeleton structure is significantly weaker, the overall performance of silicon-matrix TSPs is inferior to cobalt-matrix PDCs.
Another method of forming a TSP has been used. Specifically overcoming the different CTE of the binder's catalyst and the diamond in the face can be accomplished by catalyst-leaching (e.g., an acid treatment to leach cobalt) after fabrication. This method has been performed such that little-to-no cobalt catalytic material remains in the plate. This technique has been shown to significantly improve the plate's thermal resistances on abrasion resistance of the plate, at the cost of increasing the brittleness of the plate. (See U.S. Pat. Nos. 4,104,344, 4,288,248, and 8,020,644, all of which are incorporated by reference.) However, this method also deteriorates the usually-metallic substrate due to acid corrosion. Therefore, care should be taken to protect the substrate from acid corrosion while leaching the PDC, or other manufacturing steps are necessary in order to prepare the leached compact for use.
Therefore, there is a need for a more durable PDC that is easy to manufacture and that has the ability to withstand high temperatures, abrasion, and shear with less probability of fracture or total failure in a given amount of time, without the disadvantages of those methods that have been proposed before.